Conventionally, as this type of roller bearing, there has been provided one in which tapered rollers are placed between inner and outer rings, both end portions of an outer circumferential surface of each tapered roller being subjected to trapezoidal crowning so as to reduce edge loads that act on both end portions of the tapered roller.
However, even a conventional tapered roller bearing in which trapezoidal crowning has been applied to both end portions of an outer circumferential surface of each tapered roller as mentioned above has a problem that contact stress becomes extremely high locally at some places as shown in FIG. 5(B).
In FIG. 5(A), the abscissa shows the distance of the raceway surface of the inner ring from the raceway center of the inner ring along a generatrix, i.e., inner-ring generatrix position, while the ordinate shows the crowning depth that is a clearance between the tapered roller and raceway surface. Also, in FIG. 5(B), the abscissa shows the inner-ring generatrix position, while the ordinate shows contact stress produced between roller and inner-ring raceway surface. As can be seen from FIGS. 5(A) and 5(B), in this tapered roller bearing, contact stresses are produced, concentrated at places where the crowning starts.
FIGS. 5(A) and 5(B) assume a state in which a moment load is applied to the bearing, where the inclination angle between inner and outer rings of the bearing is set at 0.degree.6'. In this case, since contact stresses are concentrated particularly on a one-side start place of the crowning, the bearing is further shortened in life.
Because of the occurrence of stress concentration at places where the crowning starts as shown above, the conventional tapered roller bearing has a problem that its life becomes shorter when subjected to heavy load or high moment load.
It is therefore an object of the present invention to provide a roller bearing in which contact stress between rollers and raceway is uniformized by optimizing the configuration of a clearance between the rollers and the raceway.